1. Field of the Invention
This invention relates to stepper motors that can provide directional translational or rotary motion in discrete displacements. More particularly, one embodiment of the present invention relates to a pneumatic stepper motor which is constructed from materials that can be used in all classes of medical imaging equipment.
2. Description of Prior Art
Noninvasive, diagnostic imaging techniques, such as ultrasound, x-ray and magnetic resonance imaging (MRI) are widely used in medicine. They are used to produce cross-sectional images of a patient's organs and other internal body structures.
MRI typically involves the patient lying inside a large, hollow cylinder containing a strong electromagnet, which generates a strong and uniform magnetic field that causes the electrons in a patient's body to spin in a uniform and predictable manner. The MRI equipment can then manipulate the spinning electrons and use the resulting information to generate an image of the inside of a patient's body.
However, difficulties are encountered in obtaining accurate images when disruptions and deflections in the magnetic field are experienced due to the presence in the field of materials that produce a magnetic field and/or are susceptible to producing their own magnetic fields when placed within an external magnetic field.
One source of magnetic field distortion can be equipment such as motors that are in the vicinity of the MRI machine. Motors are generally formed with materials that produce a magnetic field. Examples of such materials that are commonly used in motors include iron and brass. Thus, when placed in the field generated by the MRI machine, the typical electric actuated motor can cause artifacts in the image of the patient's body. Other forms of medical imaging (e.g., x-ray and ultrasound imagers) are also seen to have similar problems of distortions in their output images due to the presence of motors in the vicinity of the imaging equipment.
This situation has been a considerable implement to the development of medical robots that can operate within a medical imaging environment. This is significant because a robot that could precisely operate within the closed bore of high intensity magnetic resonance imaging (MRI) equipment could offer a means to yield significant improvements in various types of medical procedures. For example, such a robot would make possible the performance of remote procedures within the scanner under MRI guidance. This could allow one to insert a needle precisely at the center of a small tumor visualized in the image for performing a tumor-centered biopsy. Such biopsy procedures are typically performed with randomized sampling techniques. The use of a robot could reduce the incidence of false-negative sampling.
It is possible to build pneumatic, or non-electric, actuated motors from materials that do not produce a magnetic field. However, pneumatic actuation has previously been used primarily in industrial and commercial applications for its low cost, compact size, high power to weight ratio, reliability, and low maintenance. In many cases these characteristics make it preferable over electric actuation, especially when a supply of air is readily available.
The major limitation of pneumatic actuators, rotary or linear, has been their reduced precision in controlled motion. This is mainly caused by air compressibility and friction in the valve and actuator which make the pump-line-actuator dynamic system highly nonlinear.
Novel hardware and pneumatic-servo control solutions have been proposed to deal with these problems and impressive results have been achieved in force control and rotary speed regulation. Nevertheless, these complex solutions require special care so that most of their practical applications are still limited to unregulated pneumatic motion. A new approach to a pneumatic actuator is needed to circumvent these pneumatic-servo problems and to make possible the development of a medical robot for use in medical imaging environments.
3. Objects and Advantages
There has been summarized above, rather broadly, the prior art that is related to the present invention in order that the context of the present invention may be better understood and appreciated. In this regard, it is instructive to also consider the objects and advantages of the present invention.
It is an object of the present invention to provide a stepper motor that can be used for medical applications which require the motor to be located in or in close proximity to medical imaging equipment.
It is another object of the present invention to provide a stepper motor that can be used in a surgical environment.
It is yet another object of the present invention to provide a motor that can provide precise, backlash-free motion.
It is still another object of the present invention to provide a motor that does not utilize electrical power or electrical components for its operation.
It is a further object of the present invention to provide a precise motor that can be powered by fluid power means.
These and other objects and advantages of the present invention will become readily apparent as the invention is better understood by reference to the accompanying summary, drawings and the detailed description that follows.